System and method for selecting an operation mode of a mobile platform

ABSTRACT

A method for selecting an operation mode of a mobile platform includes detecting a height grade of the mobile platform and selecting an operation mode of the mobile platform according to a result of the detecting.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 15/844,252,filed on Dec. 15, 2017, which is a continuation of InternationalApplication No. PCT/CN2015/082524, filed on Jun. 26, 2015, the entirecontents of both of which are incorporated herein by reference.

FIELD

The disclosed embodiments relate generally to mobile platform operationsand more particularly, but not exclusively, to systems and methods foroperating a mobile platform within a wide range of heights.

BACKGROUND

Unmanned Aerial Vehicles (“UAVs”) are commonly navigated and otherwiseoperated via vision technology. However, performance and precision ofthe vision technology are limited and can vary in accordance with heightof the UAV.

Currently-available vision technology can only ensure its performanceand precision within a certain height range. At lower or higher heights,the precision for operating the mobile platform is limited and cannot beensured because of inherent shortcomings of the vision technology.

In view of the foregoing reasons, there is a need for a system andmethod for effectively operating the mobile platform in a wide range ofheights.

SUMMARY

In accordance with a first aspect disclosed herein, there is set forth amethod for selecting an operation mode of a mobile platform, comprising:

detecting a height grade of the mobile platform; and

selecting an operation mode of the mobile platform according to a resultof the detecting.

In an exemplary embodiment of the disclosed methods, detecting theheight grade comprises determining a height of the mobile platformand/or a disparity between first and second images of a remote objectfrom the perspective of the mobile platform.

In another exemplary embodiment of the disclosed methods, determiningcomprises obtaining the height via a barometer, an ultrasonic detectorand/or a Global Positioning System (“GPS”).

In another exemplary embodiment of the disclosed methods, determiningcomprises acquiring the disparity between the first and second images ofthe object as captured by a binocular imaging system associated with themobile platform.

Exemplary embodiments of the disclosed methods further comprisecategorizing the operation modes based on values of the height and/ordisparity.

Exemplary embodiments of the disclosed methods further compriseinitiating the mobile platform to operate at a first height mode.

In an exemplary embodiment of the disclosed methods, the first heightmode comprises a very low altitude monocular mode.

Exemplary embodiments of the disclosed methods further compriseproviding a distance sensor of the moving platform to assist the verylow altitude monocular mode.

In an exemplary embodiment of the disclosed methods, selecting theoperation mode comprises switching the operation mode based on theheight grade, and wherein the height grade is determined based on atleast one of the determined height and the determined disparity.

In another exemplary embodiment of the disclosed methods, selecting theoperation mode comprises switching the mobile platform to a secondheight mode when the height is greater than a first height threshold.

In another exemplary embodiment of the disclosed methods, selecting theoperation mode comprises switching the mobile platform to a secondheight mode when the disparity is less than a first disparity threshold.

In another exemplary embodiment of the disclosed methods, selecting theoperation mode comprises switching the mobile platform to a secondheight mode when the height is greater than a first height threshold andthe disparity is less than the first disparity threshold.

In another exemplary embodiment of the disclosed methods, switching themobile platform to a second height mode comprises selecting a stereovision mode with a first resolution.

In another exemplary embodiment of the disclosed methods, selecting theoperation mode comprises switching the mobile platform to a third heightmode when the disparity is less than or equal to a third disparitythreshold.

In another exemplary embodiment of the disclosed methods, switching themobile platform to a third height mode comprises switching a binocularimaging device to a stereo vision mode with an enhanced resolution.

In another exemplary embodiment of the disclosed methods, selecting theoperation mode comprises switching the mobile platform to a fourthheight mode when the height is greater than a third height threshold.

In another exemplary embodiment of the disclosed methods, selecting theoperation mode comprises switching the mobile platform to a fourthheight mode when the height is greater than a third height threshold andthe disparity is less than the fifth disparity threshold.

In another exemplary embodiment of the disclosed methods, switching themobile platform to a fourth height mode comprises switching thebinocular imaging device to a high altitude monocular mode incombination with a barometer, a GPS and/or a visual measurement of avertical distance between the mobile platform and a ground level.

In another exemplary embodiment of the disclosed methods, selecting theoperation mode comprises switching the mobile platform to the thirdheight mode when the height is less than a fourth height threshold.

In another exemplary embodiment of the disclosed methods, selecting theoperation mode comprises switching the mobile platform to the thirdheight mode when the height is less than a fourth height threshold andthe disparity is greater than a sixth disparity threshold.

In another exemplary embodiment of the disclosed methods, selecting theoperation mode comprises switching the mobile platform to the secondheight mode when the disparity is greater than a fourth disparitythreshold.

In another exemplary embodiment of the disclosed methods, selecting theoperation mode comprises switching the mobile platform to the firstheight mode when the height is less than a second height threshold.

In another exemplary embodiment of the disclosed methods, selecting theoperation mode comprises switching the mobile platform to the firstheight mode when the height is less than a second height threshold andthe disparity is greater than a second disparity threshold.

In another exemplary embodiment of the disclosed methods, the seconddisparity threshold is greater than the first disparity threshold;

at least one of the first and second disparity thresholds is greaterthan at least one of the third and fourth disparity thresholds;

the third disparity threshold is greater than the fourth disparitythreshold;

at least one of the third and fourth disparity thresholds is greaterthan at least one of the fifth and sixth disparity thresholds; and

the sixth disparity threshold is greater than the fifth threshold.

In another exemplary embodiment of the disclosed methods,

the first height threshold is greater than the second height threshold;

at least one of the third and fourth height thresholds is greater thanat least one of the first and second height thresholds; and

the third height threshold is greater than the fourth threshold.

In another exemplary embodiment of the disclosed methods, determiningthe disparity of the first and second images comprises:

selecting a plurality of feature points from the first image; and

matching the feature points of the first image with points of the secondimage.

In another exemplary embodiment of the disclosed methods, the featurepoints comprise pixels of either the first image or the second image.

In another exemplary embodiment of the disclosed methods, matching theplurality of feature points comprises:

scanning the second image to identify a point of the second image thatmatches a selected feature point of the first image; and

calculating a similarity between the selected feature point of the firstimage and the point of the second image.

In another exemplary embodiment of the disclosed methods, calculatingthe similarity comprises:

building a first binary string representing a first region around theselected feature point by comparing intensities of each point pairs ofthe region to generate a first Binary Robust Independent ElementaryFeatures (“BRIEF”) descriptor;

building a second binary string representing a second region around thepoint of the second image by comparing intensities of each point pairsof the second region to generate a second BRIEF descriptor; and

determining the point of the second image matches the selected featurepoint when a hamming distance between the first BRIEF descriptor and thesecond BRIEF descriptor is less than a first hamming threshold.

In another exemplary embodiment of the disclosed methods, calculatingthe similarity comprises comparing the selected feature point of thefirst image with a three-by-three pixel area centered around the pointon the second image.

In another exemplary embodiment of the disclosed methods, comparingcomprises comparing a sum of differences for each color component ofeach pixel of color images or a sum of differences of grayscale valuesof each pixel of black and white images.

In another exemplary embodiment of the disclosed methods, determiningthe disparity comprises acquiring the disparity based on an average ofthe disparities of the feature points.

In another exemplary embodiment of the disclosed methods, determiningthe disparity comprises selecting one or more feature points andacquiring the disparity based on the disparities of the selected featurepoints.

In accordance with another aspect disclosed herein, there is set forth asystem for selecting an operation mode of a mobile platform configuredto perform the detection process in accordance with any one of previousembodiments of the disclosed methods.

In accordance with another aspect disclosed herein, there is set forth acomputer program product comprising instructions for selecting anoperation mode of a mobile platform configured to perform the detectionprocess in accordance with any one of previous embodiments of thedisclosed methods.

In accordance with another aspect disclosed herein, there is set forthan apparatus for selecting an operation mode of a mobile platform,comprising:

a binocular imaging device associated with the mobile platform; and

a processor configured for:

detecting a height grade of the mobile platform; and

selecting an operation mode of the mobile platform according to a resultof the detecting.

In an exemplary embodiment of the disclosed apparatuses, the processoris configured to determine a height of the mobile platform and/or adisparity between first and second images of a remote object from theperspective of the mobile platform.

Exemplary embodiments of the disclosed apparatuses further comprise abarometer associated with the mobile platform for obtaining the heightof the mobile platform.

Exemplary embodiments of the disclosed apparatuses further comprise anultrasonic detector associated with the mobile platform for obtainingthe height of the mobile platform.

Exemplary embodiments of the disclosed apparatuses further comprise aGPS associated with the mobile platform for obtaining the height and/orlocation of the mobile platform.

In an exemplary embodiment of the disclosed apparatuses, the processoris configured to acquire the disparity between the first and secondimages of the object as captured by a binocular imaging systemassociated with the mobile platform.

In an exemplary embodiment of the disclosed apparatuses, the operationmodes of the mobile platform are categorized based on height valuesand/or the disparity values.

In an exemplary embodiment of the disclosed apparatuses, the processoris configured to initialize the mobile platform to operate at a firstheight mode.

In an exemplary embodiment of the disclosed apparatuses, the firstheight mode comprises a very low altitude monocular mode.

In an exemplary embodiment of the disclosed apparatuses, a distancesensor of the moving platform is provided to assist the very lowaltitude monocular mode.

In another exemplary embodiment of the disclosed apparatuses, theprocessor is configured to switch the operation mode based on the heightgrade, and wherein the height grade is determined based on at least oneof the determined height and the determined disparity.

In another exemplary embodiment of the disclosed apparatuses, theprocessor is configured to switch to a second height mode when theheight is greater than a first height threshold.

In another exemplary embodiment of the disclosed apparatuses, theprocessor is configured to switch to a second height mode when thedisparity is less than a first disparity threshold.

In another exemplary embodiment of the disclosed apparatuses, theprocessor is configured to switch to a second height mode when theheight is greater than a first height threshold and the disparity isless than the first disparity threshold.

In another exemplary embodiment of the disclosed apparatuses, the secondheight mode comprises a stereo vision mode with a first resolution.

In another exemplary embodiment of the disclosed apparatuses, theprocessor is configured to switch to a third height mode when thedisparity is less than or equal to a third disparity threshold.

In another exemplary embodiment of the disclosed apparatuses, the thirdheight mode is a stereo vision mode with an enhanced resolution.

In another exemplary embodiment of the disclosed apparatuses, theprocessor is configured to switch to a fourth height mode when theheight is greater than a third height threshold.

In another exemplary embodiment of the disclosed apparatuses, theprocessor is configured to switch to a fourth height mode when theheight is greater than a third height threshold and the disparity isless than the fifth disparity threshold.

In another exemplary embodiment of the disclosed apparatuses, the fourthheight mode comprises is a high altitude monocular mode in combinationwith a barometer, a GPS and/or a visual measurement of a verticaldistance between the mobile platform and a ground level.

In another exemplary embodiment of the disclosed apparatuses, theprocessor is configured to switch to the third height mode when theheight is less than a fourth height threshold.

In another exemplary embodiment of the disclosed apparatuses, theprocessor is configured to switch to the third height mode when theheight is less than a fourth height threshold and the disparity isgreater than a sixth disparity threshold.

In another exemplary embodiment of the disclosed apparatuses, theprocessor is configured to switch to the second height mode when thedisparity is greater than a fourth disparity threshold.

In another exemplary embodiment of the disclosed apparatuses, theprocessor is configured to switch the first height mode when the heightis less than a second height threshold.

In another exemplary embodiment of the disclosed apparatuses, theprocessor is configured to switch the first height mode when the heightis less than a second height threshold and the disparity is greater thana second disparity threshold.

In another exemplary embodiment of the disclosed apparatuses, the seconddisparity threshold is greater than the first disparity threshold;

one or both of the first and second disparity thresholds are greaterthan one or both of the third and fourth disparity thresholds;

the third disparity threshold is greater than the fourth disparitythreshold;

one or both of the third and fourth disparity thresholds are greaterthan one or both of the fifth and sixth disparity thresholds; and

the sixth disparity threshold is greater than the fifth threshold.

In another exemplary embodiment of the disclosed apparatuses, the firstheight threshold is greater than the second height threshold;

any one of the third and fourth height thresholds is greater than thefirst and second height thresholds; and

the third height threshold is greater than the fourth threshold.

In another exemplary embodiment of the disclosed apparatuses, theprocessor is configured to determine the height of an Unmanned AerialVehicle (“UAV”) and the disparity from the perspective of the UAV, and

wherein the processor is configured to select an operation mode of theUAV according to the determining.

In another exemplary embodiment of the disclosed apparatuses, theprocessor is configured to select a plurality of feature points on thefirst image and to match the plurality of feature points of the firstimage with points of the second image.

In another exemplary embodiment of the disclosed apparatuses, thefeature points comprise pixels of either the first image or the secondimage.

In another exemplary embodiment of the disclosed apparatuses, thedisparity is at least five pixels and no more than one fifth of a widthof the first image or the second image.

In another exemplary embodiment of the disclosed apparatuses, theprocessor is configured to scan the second image to identify a point ofthe second image that matches a selected feature point of the firstimage and to calculate a similarity between the selected feature pointof the first image and the point.

In another exemplary embodiment of the disclosed apparatuses, theprocessor is configured for:

building a first binary string representing a first region around theselected feature point by comparing intensities of each point pairs ofthe region to generate a first Binary Robust Independent ElementaryFeatures (“BRIEF”) descriptor;

building a second binary string representing a second region around thepoint of the second image by comparing intensities of each point pairsof the second region to generate a second BRIEF descriptor; and

determining the point of the second image matches the selected featurepoint when a hamming distance between the first BRIEF descriptor and thesecond BRIEF descriptor is less than a first hamming threshold.

In another exemplary embodiment of the disclosed apparatuses, thesimilarity is calculated by comparing the selected feature point of thefirst image with a three-by-three pixel area centered around the pointon the second image.

In another exemplary embodiment of the disclosed apparatuses, thethree-by-three pixel area is compared by a sum of differences for eachcolor component of each pixel of color images or a sum of differences ofgrayscale values of each pixel of black and white images.

In another exemplary embodiment of the disclosed apparatuses, thedisparity is determined based on an average of the feature disparities.

In another exemplary embodiment of the disclosed apparatuses, theprocessor is configured to select one or more feature points and toacquire the disparity based on the features disparities of the selectedfeature points.

In accordance with another aspect disclosed herein, there is set forth amethod for determining an operation mode of a mobile platform,comprising:

detecting a height grade of the mobile platform;

selecting one or more sensors based on a result of the detecting; and

obtaining measurements from the selected sensors,

wherein the height grade is selected from a group of four height grades.

In another exemplary embodiment of the disclosed methods, selecting theone or more sensors comprises selecting one image sensor at a firstheight grade.

In another exemplary embodiment of the disclosed methods, selecting theone or more sensors comprises selecting one image sensor and a distancesensor at a first height grade.

In another exemplary embodiment of the disclosed methods, the distancesensor comprises an ultrasonic detector and/or a laser detection device.

In another exemplary embodiment of the disclosed methods, selecting theone or more sensors further comprises selecting at least two imagesensors at a second height grade,

wherein the at least two image sensors have a first resolution.

In another exemplary embodiment of the disclosed methods, selecting theone or more sensors further comprises selecting at least two imagesensors with a second resolution at a third height grade, the secondresolution being an enhanced resolution.

In another exemplary embodiment of the disclosed methods, the secondresolution is greater than the first resolution.

In another exemplary embodiment of the disclosed methods, selecting theone or more sensors further comprises selecting one image sensor and oneheight sensor at a fourth height grade.

In another exemplary embodiment of the disclosed methods, the heightsensor comprises a barometer and/or a Global Positioning System (“GPS”).

In accordance with another aspect disclosed herein, there is set forth aflying operation system of a mobile platform, comprising:

a height sensor for detecting a height grade of the mobile platform;

a processor configured to select one or more sensors based on thedetected height grade and to obtain measurements from the selectedsensors,

wherein the height grade is selected from a group of four height grades.

In another exemplary embodiment of the disclosed systems, the processoris configured to select one image sensor at a first height grade.

In another exemplary embodiment of the disclosed systems, the processoris configured to select one image sensor and a distance sensor at afirst height grade.

In another exemplary embodiment of the disclosed systems, the heightsensor comprises a distance sensor, and wherein the distance sensorcomprises an ultrasonic detector and/or a laser detection device.

In another exemplary embodiment of the disclosed systems, the processoris configured to select at least two image sensors at a second heightgrade,

wherein the at least two image sensors have a first resolution.

In another exemplary embodiment of the disclosed systems, the processoris configured to select at least two image sensors with a secondresolution at a third height grade, the second resolution being anenhanced resolution.

In another exemplary embodiment of the disclosed systems, the secondresolution is greater than the first resolution.

In another exemplary embodiment of the disclosed systems, the processoris configured to select one image sensor and one height sensor at afourth height grade.

In another exemplary embodiment of the disclosed systems, the heightsensor comprises a barometer and/or a Global Positioning System (“GPS”).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 an exemplary top-level flowchart, illustrating an embodiment of amethod for selecting an operation mode in a wide range of heights.

FIG. 2 is an exemplary schematic diagram, illustrating a mobile platformequipped with devices to realize the method of FIG. 1, wherein suchdevices include a barometer, a GPS, an ultrasonic detector and a stereovision system.

FIG. 3 is an exemplary flowchart of another embodiment of the method ofFIG. 1, wherein the method includes categorizing operation modes fordifferent heights.

FIG. 4 is an exemplary block diagram of another embodiment of the methodof FIG. 3, wherein the method categorizes four operation modes based onheights.

FIG. 5 is an exemplary block diagram of another embodiment of the methodof FIG. 1, wherein the height and the disparity information is used todecide a working operation mode.

FIG. 6 is an exemplary block diagram of another embodiment of the mobileplatform of FIG. 2, wherein the mobile platform uses the barometer, theultrasonic detector and/or the GPS for obtaining the height information.

FIG. 7 is an exemplary top-level diagram, illustrating anotherembodiment of the mobile platform of FIG. 2, wherein a processorcollects condition data and controls the operation modes.

FIG. 8 is an exemplary flowchart of another embodiment of the method ofFIG. 1, illustrating switching conditions among four different operationmodes.

FIG. 9 is an exemplary detail drawing illustrating an embodiment of astereoscopic imaging method, wherein the disparity of the method of FIG.1 is decided.

FIG. 10 is an exemplary diagram of another embodiment of the method ofFIG. 9, illustrating an exemplary method for matching two images with anoverlapping area.

FIG. 11 is an exemplary diagram illustrating another embodiment of themethod of FIG. 9, wherein a first image is matched with a second imagewith a plurality of feature points.

FIG. 12 is an exemplary diagram illustrating another embodiment of themethod of FIG. 11, wherein each feature point is matched by calculatinga similarity.

FIG. 13 is an exemplary top-level flowchart of another embodiment of themethod for determining an operation mode, wherein sensors of the mobileplatform are selected for each of the four operation modes of FIG. 4.

FIG. 14 is an exemplary flowchart of another embodiment of the method ofFIG. 13, illustrating a manner for selecting the sensor based upon eachof the operation modes.

FIG. 15 is an exemplary top-level diagram illustrating still anotherembodiment of a flying operation system of the mobile platform of FIG.2, wherein a processor selects sensors of the mobile platform for eachof four operation modes.

It should be noted that the figures are not drawn to scale and thatelements of similar structures or functions are generally represented bylike reference numerals for illustrative purposes throughout thefigures. It also should be noted that the figures are only intended tofacilitate the description of the embodiments. The figures do notillustrate every aspect of the described embodiments and do not limitthe scope of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Navigation of Unmanned Aerial Vehicles (“UAVs”) commonly is performed byusing stereo vision technology for operating the UAVs. However, theprecision of stereo vision technology is limited and can vary inaccordance with height.

Stereo vision systems typically perform navigation by considering anoverlapping area of a scene as viewed by each of two lenses of thestereo vision system. A baseline length between the lenses ofconventional stereo vision systems typically is between four centimetersand twenty centimeters. The applicable height range of the stereo visiontechnology, however, is restricted by the baseline length. In otherwords, the range of measurable height is limited by the baseline length.

The overlapping area of the scene is relied on to operate the UAV. Atlow altitude, for example, a distance between the lenses of thebinocular imaging system and the ground is too short to form a usableoverlapping area between each scene viewed by the lenses of thebinocular imaging device. Whereas, at very high altitude, a distancebetween the lenses of the stereo vision system and the ground is toolong. In such case, the long distance generates a short baseline betweenthe two lenses of the stereo vision system, resulting inaccuratecalculation results.

Since currently-available stereo vision navigation systems arerestricted by baseline lengths, a mobile system and method that can meetthe requirements of operating the UAV at various heights by switchingamong operation modes based on a height of the mobile system and adisparity can prove desirable and provide a basis for accuratemeasurement of depth, for systems such as UAV systems and other mobilesystems. This result can be achieved, according to one embodimentdisclosed in FIG. 1.

Referring now to FIG. 1, an exemplary embodiment of a method 100 forselecting an operation mode of a mobile platform 200 (shown in FIG. 2)in a wide range of heights. In

FIG. 1, at 120, a height 121 and/or a disparity 122 can be detected asbases for determining an operation mode for the mobile platform 200. Theheight 121 and/or the disparity 122 can represent a height grade. Insome embodiments, such detection can be conducted in real-time and/or ina time-delayed manner. The height 121 is associated with an elevationinformation, such as flying height, or altitude, of the mobile platform200. The disparity 122 represents a difference in image location of anobject depicted in two images or frames. The disparity 122 can bedecided statically and/or dynamically in the manner shown and describedbelow with reference to FIGS. 9-12. The mobile platform 200 can compriseany form of aerial vehicle that can have an elevation while such mobileplatform 200 is in operation. The height 121 can be determined in themanner shown and described below with reference to FIG. 6.

At 130, the mobile platform 200 can use the acquired height grade, i.e.the height 121 and/or the disparity 122, to select or switch amongseveral predetermined operation modes 131. The operation modes 131 cancomprise operations involving various devices associated with the mobileplatform 200, which can be included at any time. Such devices are shownand described below with reference to FIGS. 6 and 7. The selection orswitching of operation modes 131 will be shown and described in detailwith reference to FIG. 8.

Although shown and described as using the height 121 and/or thedisparity 122 as the criteria for selecting or switching operation modesfor illustrative purposes only, other suitable condition data can beused for the criteria of selecting or switching among operation modes.

FIG. 2 shows a mobile platform 200 with devices 251-254 for detectingconditions that can be bases to realize the method 100 by switchingoperation modes 131. In FIG. 2, the devices 251-254 can include at leasta barometer 251, one or more ultrasonic detectors 252, a GPS 253 and abinocular imaging device 254. Among the devices 251-254, the barometer251, the ultrasonic detector 252 and/or the GPS 253 can be used todetect the height 121 (or altitude) of the mobile platform 200, and thebinocular imaging device 254 can be an information source of thedisparity 122. In FIG. 2, the ultrasonic detector 252 can be used todetect a distance to an object 288 that can be the ground. Therefore,the distance between the ultrasonic detector 252 and the object 288 canrepresent a vertical height 121 of the mobile platform 200 relative tothe ground level.

In FIG. 2, the barometer 251 can be installed on top of a body 260 ofthe mobile platform 200. The ultrasonic detectors 252 can be arrangedaround a lower part of the body 260. The GPS 253 can be installed in thebody 260 of the mobile platform 200. The binocular imaging device 254can be arranged under the body 260. However, under this disclosure, thebarometer 251 and the GPS 253 can be disposed on any part of the mobileplatform 200, such as inside the body 260, under the body 260 or anyside of the body 260 etc. The ultrasonic detectors 252 can be disposedanywhere around the body 260. The binocular imaging device 254 can bedisposed at any suitable position of the lower part of the body 260.

Although shown and described as using the devices 251-254 for purposesof illustrations only, any other suitable devices can also be used fordetecting the conditions for determining the switching among theoperation modes 131. The mobile platform 200 can comprise anyconventional type of mobile platform that can have an elevation and isillustrated in FIG. 2 as comprising an unmanned aerial vehicle UAV 250for purposes of illustration only and not for purposes of limitation.

FIG. 3 shows another exemplary embodiment of the method 100 forselecting an operation mode in a wide range of heights. In FIG. 3, themethod 100 can comprise a procedure of categorizing operation modes, at310. The operation modes can be categorized, for example, based upondifferent height grades, i.e. height range and/or disparity values. Asdiscussed above, currently-available single mode operations cannot meetrequirements of different heights, for example, a binocular system usingstereo vision technology cannot satisfy requirements for a highaltitude/height and a very low altitude/height. On the other hand, otheravailable operation modes of a mobile platform 200 can be more suitablefor the high altitude/height or the low altitude/height.

At different heights or altitudes, a variation of operation modes can beused to operate the mobile platform 200. For the purposes of operatingthe mobile platform 200 at all heights, the operation modes can becategorized according to several height grades. Additional detail of thecategorization will be shown and described below with reference to FIG.4.

Although described as categorizing the operation modes according todifferent height grades for purposes of illustrations only, thecategorization under this disclosure can based on any other suitableinformation, such as based on a combination of the height 121 and thedisparity 122.

FIG. 4 shows an embodiment of the categorizing operation modes into fourmodes for the method 100. In FIG. 4, a first height mode 411, a secondheight mode 412, a third height mode 413, and a fourth height mode 414can be provided in accordance with different height grades. The fourthheight mode 414 is designed to be used with, for example, a fourthheight range of twenty meters (20 m) and above. Under the fourth heightmode 414, the mobile platform 200 (shown in FIG. 2) can work with ahigh-altitude monocular mode. Under the high-altitude monocular mode, inorder to determine the height 121, a depth of an object can bedetermined, for example, with a combination of a barometer 251, a GPS253 and/or vision detection. An operation mode of the mobile platform200 can be determined based on the height information.

The third height mode 413 is designed to be used with, for example, athird height range of three and half meters (3.5 m) to twenty meters (20m). Within the third height range, a binocular device with a normalresolution of three hundred and twenty by two hundred and forty(320×240) cannot meet the requirements of detecting the depth andselecting an operation mode of the mobile platform 200. To deal with theissue, under the third height mode 413, an enhanced resolution binocularmode can be utilized to determine the height 121 and selecting anoperation mode of the mobile platform 200. Under the enhanced resolutionbinocular mode, the resolution can be at least six hundred and fourth byfour hundred and eighty (640×480).

The second height mode 412 is designed to be used with, for example, asecond height range of fifty centimeters (50 cm) to three and a halfmeters (3.5 m). Within the second height range, the second height mode412 can use a normal-resolution binocular mode, which can use aresolution of three hundred and twenty by two hundred and forty(320×240).

The first height mode 411 is designed to be used with, for example, afirst height range of ten centimeters (10 cm) to fifty centimeters (50cm). Within the first height range, there may not be enough overlappingbetween images acquired with two lenses for a binocular system becauseof a short distance between the lenses and an object of interest.Therefore, under the first height mode 411, a very low altitudemonocular mode can be used; wherein, other distance sensors can beemployed to detect a distance between an optical center of a lens andthe ground level, i.e. the object depth, for selecting an operation modeof the mobile platform 200.

Although shown and described as categorizing operation modes into fourcategories for purposes of illustration only, any suitable number ofcategories can be utilized under the present disclosure. In addition tothe height 121 to the ground, the present disclosure can use otherconditions in categorizing and/or switching among the operation modes.Such conditions can comprise the disparity 122.

FIG. 5 shows another exemplary embodiment of the method 100, wherein aheight 121 and/or a disparity 122 can be used for deciding an operationmode 131. The height 121 represents a vertical distance between themobile platform 200 (shown in FIG. 2) and the ground level. The height121 can be acquired via a barometer 251, an ultrasonic detector 252and/or a GPS 253, in a manner shown and described below with referenceto FIG. 6. As shown and described with reference to FIG. 1, thedisparity 122 represents a difference in image location of an object intwo images or frames. The disparity 122 can be determined in a mannershown and described below with reference to FIGS. 9-12.

At 230, the height 121 and the disparity 122 information can becombined. The combined information can be used in deciding the operationmode 131, at 240. Although shown and described as using the combinedinformation to decide the operation mode 131, either the height 121 orand disparity 122 can be used separately in deciding the operation mode131.

FIG. 6 shows an exemplary embodiment of the mobile platform 200 showingobtaining the height 121, at 120, in the method 100. In FIG. 6, abarometer 251, an ultrasonic detector 252 and/or a GPS 253 can be usedto obtain the height 121 of the mobile platform 200 (collectively shownin FIG. 2). The barometer 251 can be any type of barometer or pressurealtimeter, which is commercially available from the market, fordetermining the height 121 based on a measurement of atmosphericpressure. Such a barometer 251 can comprise a water-based barometer, amercury barometer, a vacuum pump oil barometer, an aneroid barometer, abarograph or an MEMS barometer. The barometer 251 can also include othertypes of barometers, such as a storm barometer.

Additionally and/or alternatively, the ultrasonic detector 252 can beused to detect a distance 121 of an object 288 (shown in FIG. 2) in thesurroundings by emitting ultrasonic waves and receiving ultrasonic wavesreflected from the object 288. The distance 121 can be a distance to theground level, where the object 288 is the ground. The ground level 880can be the actual ground, a water level or the ground with anystructure. Such ultrasonic detector 252 can comprise anycommercially-available ultrasonic sensors. Although shown and describedas using a single ultrasonic detector 252 for detecting the object 288in one direction for purposes of illustration only, multiple ultrasonicdetectors 252 can be provided for detecting an object 288 in multipledirections.

The GPS 253 is a space-based satellite navigation system that canprovide a location, a height and/or time information anywhere on or nearthe earth where there is an unobstructed line of sight to four or moreGPS satellites. The GPS 252 can comprise any GPS devices commerciallyavailable from the market. The location can be provided by the GPS 253as longitude and latitude. The height can be a height in meters or feetto the ground level.

The height 121, applicable under this disclosure, can be any verticaldistance in a range of twenty-five centimeters (25 cm) to over onehundred meters (100 m) to the ground level. As shown and described withreference to FIG. 4, the height 121 can be categorized into a firstheight, a second height, a third height, and a fourth height under thisdisclosure. Although shown and described as using a barometer 251, anultrasonic detector 252 or a GPS 253 for detecting the height 121 forpurposes of illustration only, other suitable detecting devices can beused for detecting the height 121 of the mobile platform 200.

FIG. 7 illustrates another exemplary embodiment of the mobile platform200 of FIG. 2. In FIG. 7, a processor 910 can be connected with thebarometer 251, the ultrasonic detector 252, the GPS 253 and thebinocular imaging device 254 to collect condition data and controls theoperation modes for implementing the method 100. The processor 910 canbe a processor associated with the mobile platform for controlling themobile platform 200. The binocular imaging device 254 can be an imagingdevice with binocular lenses that can be used to capture two images ofan object simultaneously.

In some embodiments of the mobile platform 200, the processor 910 can beprovided for obtaining and processing the information obtained from thebarometer 251, the ultrasonic detector 252, the GPS 253 and/or thebinocular device 254. Such information includes the height 121 and thedisparity 122 (collectively shown in FIG. 1). The processor 910 candetermine which operation mode 131 can be selected based on theinformation. Additional detail of determining the operation mode 131will be shown and described below with reference to FIG. 8.

The processor 910 can comprise any commercially available processingchip or be any custom-designed processing chips specially produced forthe apparatus 900 for selecting an operation mode of the mobile platform200. Additionally and/or alternatively, the processor 910 can includeone or more general purpose microprocessors (for example, single ormulti-core processors), application-specific integrated circuits,application-specific instruction-set processors, data processing units,physics processing units, digital signal processing units, coprocessors,network processing units, audio processing units, encryption processingunits, and the like. The processor 910 can be configured to perform anyof the methods described herein, including but not limited to, a varietyof operations relating to operation mode selection. In some embodiments,the processor 910 can include specialized hardware for processingspecific operations relating to operation mode selection.

FIG. 8 shows another exemplary embodiment for the method 100, where fouroperation modes can be selected (or switched) based on the height 121and/or the disparity 122. Upon lifting off, the mobile platform 200(shown in FIG. 2) can operate at a first height. An apparatus forselecting an operation mode of the mobile platform 200 can work with acorresponding operation mode, i.e. a first height mode 411. As shown anddescribed with reference to FIG. 4, the first height mode 411 is a verylow altitude monocular mode combining with a distance sensor (not shown)for selecting an operation mode of the mobile platform 200.

When operating under the first height mode 411 and two conditions aremet, at 930, the mobile platform 200 can switch to a second height mode412. The two conditions can include that the disparity 122 of thebinocular imaging device 254 is less than or equal to a first disparitythreshold Td1 and the height 121 of the mobile platform 200 elevatesabove a first height threshold Th1. In another embodiment, the operationmode can be switched from the first height mode 411 to the second heightmode 412 when only the height 121 of the mobile platform 200 elevatesabove a first height threshold Th1.

The first disparity threshold Td1 can be selected from a first disparityrange of sixty-two centimeters (62 cm) to eighty-two centimeters (82cm), and, in some embodiments, to be seventy-two centimeters (72 cm).The first height threshold Th1 can be selected from a value in a firstheight range of twenty centimeters (20 cm) to eighty centimeters (80 cm)and, in some embodiments, to be fifty centimeters (50 cm).

When the disparity 122 of the binocular imaging device of the stereovision system is less than or equal to a third disparity threshold Td3the mobile platform 200 can switch to a third height mode 413. As shownand described with reference to FIG. 4, the third height mode 413 cancomprise a high resolution binocular mode.

The third disparity threshold Td3 can be selected from a third disparityrange of five centimeters (5 cm) to fifteen centimeters (15 cm) and, insome embodiments, to be ten centimeters (10 cm).

When two conditions are met, at 934, the operation mode can be switchedto a fourth height mode 414. The two conditions can comprise that thedisparity 122 of the binocular imaging device of the stereo visionsystem being less than or equal to a fifth disparity threshold Td5 andthe height of the mobile platform 200 elevating above a third heightthreshold Th3. The fourth height mode 414 can comprise a high altitudemonocular operation mode, which can utilize a barometer, a GPS and/orvision detector as shown and described above with reference to FIG. 4.In another embodiment, the operation mode can be switched from the thirdheight mode 413 to the fourth height mode 414 when only the height 121of the mobile platform 200 elevates above a third height threshold Th3.

The fifth disparity threshold Td5 can be selected from a value in afifth disparity range of one centimeter (1 cm) to three centimeters (3cm), and, in some embodiments, to be two centimeters (2 cm). The thirdheight threshold Th3 can be selected from a value in a third heightrange of fifteen meters (15 m) to twenty-five meters (25 m) and, in someembodiments, to be twenty meters (20 m).

When operating with the fourth height mode 414, the mobile platform 200can switch to other operation modes when any of certain conditions 931,933 is satisfied. At 931, when the disparity 122 is greater than equalto a sixth disparity threshold Td6 and the height 121 of the mobileplatform 200 is less than or equal to a fourth threshold Th4, forexample, the mobile platform 200 can switch to the third height mode413. In another embodiment, the mobile platform 200 can switch to thethird height mode 413 when only the height 121 of the mobile platform200 becomes less than or equal to the fourth threshold Th4.

At 933, when the disparity 122 is greater than or equal to a fourthdisparity threshold Td4, the mobile platform 200 can switch to thesecond height mode 412.

The sixth disparity threshold Td6 can be selected from a value in asixth disparity range of one and a half centimeters (1.5 cm) to fourcentimeters (4 cm), and, in some embodiments, to be two and a halfcentimeters (2.5 cm). The fourth height threshold, Th4, can be selectedfrom a value in a fourth height range of fifteen meters (15 m) totwenty-two meters (22 m) and, in some embodiments, to be eighteen meters(18 m). The fourth disparity threshold Td4 can be selected from a valuein a fourth disparity range of nine centimeters (9 cm) to fifteencentimeters (15 cm) and, in some embodiments, to be twelve centimeters(12 cm).

When operating at the third height mode 413, if the disparity 122 getsgreater than or equal to the fourth disparity threshold Td4, the mobileplatform 200 can switch to the second height mode 412.

When operating with the second height mode 412, the mobile platform 200can switch to the first height mode 411 when conditions at 935 aresatisfied. At 935, when the disparity 122 is greater than or equal to asecond disparity threshold Td2 and the height 121 of the mobile platform200 is less than or equal to a second height threshold Th2, the mobileplatform 200 can switch to the first height mode 411. In anotherembodiment, the mobile platform 200 can switch to the first height mode411 when only the height 121 of the mobile platform 200 becomes lessthan or equal to the second threshold Th2.

The second disparity threshold Td2 can be selected from a value in asecond disparity range of sixty centimeters (60 cm) to eightycentimeters (80 cm), and, in some embodiments, to be seventy centimeters(70 cm). The second height threshold, Th2, can be selected from a valuein a second height range of twenty-five centimeters (25 cm) tosixty-five centimeters (65 cm), and, in some embodiments, to beforty-five centimeters (45 cm).

The second disparity threshold Td2 can be greater than the firstdisparity threshold Td1. One or both of the first and second disparitythresholds Td1, Td2 can be greater than one or both of the third andfourth disparity thresholds Td3, Td4. The first height threshold Th1 canbe greater than the second height threshold Th2. One or both of thefirst and second height thresholds Th1, Th2 can be greater than one orboth of third and fourth height thresholds Th3, Th4. The third disparitythreshold Td3 can be greater than the fourth disparity threshold Td4.One or both of the third and fourth disparity thresholds Td3, Td4 can begreater than one or both of the fifth and sixth disparity thresholdsTd5, Td6. The sixth disparity threshold Td6 can be greater than thefifth disparity threshold Td5.

FIG. 9 shows an exemplary method 700 for ascertaining a binoculardisparity between two stereoscopic images 520 a, 520 b, acquired by twolenses 510 a, 510 b, of an object 598 of interest. A method oftriangulation can be used to ascertain the disparity d between theimages 520 a and 520 b. Specifically, the position of the object 598 ofinterest having an index i, represented by its coordinates (X_(i),Y_(i), Z_(i)), can be given as follows:

$\begin{matrix}{{X_{i} = {\frac{T}{d}\left( {x_{i}^{l} - c_{x}} \right)}},} & {{Equation}\mspace{14mu} (1)} \\{{Y_{i} = {\frac{T}{d}\left( {y_{i}^{l} - c_{y}} \right)}},} & {{Equation}\mspace{14mu} (2)} \\{{Z_{i} = {\frac{T}{d}f}},} & {{Equation}\mspace{14mu} (3)}\end{matrix}$

where c_(x), and c_(y) represent respective center O_(l), O_(r)coordinates of the lenses 510 a and 510 b, and y_(i) represent thecoordinates of the object 598 of interest in each of the images 520 aand 520 b respectively, Tis the baseline (in other words, the distancebetween the center coordinates of the lenses 510 a and 510 b), f is arectified focal length of the lenses 510 a and 510 b, i is an index overmultiple objects of interest 598 and/or over multiple feature points 355(shown in FIG. 10) of the object 598 of interest, and d is the binoculardisparity between the images 520 a and 520 b, represented here as:

d _(i) =x _(i) ^(l) −x _(i) ^(r)   Equation (4)

Based on the discussion for FIG. 9, the disparity d can be calculated bymatching the point X_(r) on the second image 520 b with X_(l) of thefirst image 520 a, wherein X_(i) is a known element. In FIG. 9, anexemplary embodiment of locating the matching point X_(r) on the secondimage 520 b is set forth for illustrative purposes only. In FIG. 9,I^(L) represents the first image 520 a, and I^(R) represents the secondimage 520 b of the same object 598 of interest. A point x_(i) ^(l) thefirst image 520 a can be known, and a matching point x_(i) ^(r) on thesecond image 520 b can be defined as a point that is “most similar” tothe point x^(l) _(i) of the first image 520 a, which can be representedwith the following equation:

d=argmin_(d) |I ^(L)(x _(l))−I ^(R)(x _(l) +d)|,   Equation (5)

where d represents the disparity of the two lenses 510 a, 510 b, I^(L)refers to the first image 520 a, I^(R) refers to the second image 520 bof the same object 598 of interest, x_(l) is the point x_(i) ^(l) of thefirst image 520 a.

Because of possible matching errors to ascertain matching accuracy andvision range, the disparity d cannot be less or greater than certainpredetermined values. In some embodiments, the disparity d is greaterthan 5 pixels and less than one fifth of a width of the second image 520b, which can be the same size with the first image 520 a. As anillustrative example, suppose f=480, T=0.15 m, and image resolution is320×240 pixels, an effective vision range of 1.5 m to 15.4 m can bededucted.

FIG. 10 illustrates an exemplary embodiment of the method 700 formatching a point of the second image 520 b with a corresponding point355 of the first image 520 a. In FIG. 10, a three-by-three pixel blockis taken with the compared point in the center from each of the images520 a, 520 b. When the first and second images 520 a and 520 b are colorimages, values of color components can be compared for each pixel of thethree-by-three pixel block. Conversely, when the images 520 a and 520 bare black and white images, greyscale values for each pixel can becompared. Based on Equation 5, the point with smallest sum of valuedifferences for all nine pixels can be selected as the matching point.This process can be repeated for all selected feature points on thefirst image 520 a.

In some embodiments, a method of using Binary Robust IndependentElementary Features (“BRIEF”) descriptors can be used for matching thepoint of the second image 520 b with the corresponding point 355 of thefirst image 520 a. In an exemplary embodiment, a first binary string,representing a first region around the selected feature point of thefirst image 520 a, can be built by comparing intensities of each pointpairs of the region. The first binary string can be the first BRIEFdescriptor of the selected feature point of the first image 520 a.

Similarly, a second binary string representing a second region aroundthe point 355 of the second image 520 b can be built by comparingintensities of each point pairs of the second region. The second binarystring can be a second BRIEF descriptor.

A similarity between the selected feature point of the first image 520 aand the point 355 of the second image 520 b can be calculated bycomparing a hamming distance between the first BRIEF descriptor and thesecond BRIEF descriptor. The point 355 of the second image 520 b can bedetermined as matching the selected feature point of the first image 520a when a hamming distance between the first BRIEF descriptor and thesecond BRIEF descriptor is less than a first hamming threshold.

Turning now to FIG. 11, an exemplary embodiment of the method 700 foracquiring the disparity d via feature points 355 of the object 598 ofinterest is illustrated. At 922, a plurality of feature points 355 onthe object 598 of interest can be selected. The feature points 355 canbe selected using one or more of a variety of different methods. In oneexemplary embodiment, the feature points 355 can be identified aspre-defined shapes of the object 598 of interest. In another embodiment,the feature points 355 can be recognized as one or more portions of theobject 598 of interest having a particular color or intensity. Inanother embodiment, the feature points 355 can be selected as randomportions of the object 598 of interest. In another embodiment, thefeature points 355 can be selected at regularly spaced intervals on theobject 598 of interest, for example, every pixel, every other pixel,every third pixel, every fourth pixel, and so forth. The feature points355 can take varying shapes and sizes, as desired. In some embodiments,a combination of methods described above can be used to select thefeature points 355.

At 924, the selected feature points 355 can be matched from the firstimage 520 a onto the second image 520 b. In some embodiments, matchingof the feature points 355 consists of two procedures as shown in FIG.12. In FIG. 12, at 924A, a feature point 355 of the first image canselected. A matching point can be scanned starting from a calculatedpoint and along a line parallel to the centered line of the lenses 510a, 510 b. The matching starting point can be calculated based on thecoordinates of the point on the first image 520 a, the direction and/orthe length of the baseline. Although in some embodiments limited to onlyone direction along the selected line, the scanning can be performed inany of one or more predetermined directions.

At 924B, while scanning for each point, a similarity is calculatedbetween two points in the manner shown and described above in detailherein with reference to FIG. 10, and the point 355 of the second image520 b with the minimum sum of differences with the feature point 355 ofthe first image 520 a can be selected as a matching point correspondingto the selected feature point 355.

Returning to FIG. 11, a feature disparity d between each feature points355 of the two images 520 a and 520 b can be found, at 926. Any of avariety of methods can be used to determine the disparity d. In oneembodiment, the disparity d can be found based on an average of thedisparities d for each of the feature points 355. Exemplary types ofaverages can include an arithmetic mean, a geometric mean, a median,and/or a mode without limitation. In another embodiment, the disparity dcan be found by selecting one or more of the feature points 355 andacquiring the disparity d based on the selected feature points 355.

FIG. 13 illustrates an embodiment of a method 300 for determining anoperation mode of the mobile platform 200 (shown in FIG. 15), whereincertain sensors 360 (shown in FIG. 15) can be selected for each of thefour height modes 411-414 (shown in FIG. 4) based on a height grade. InFIG. 13, at 320, the height grade of the mobile platform 200 can bedetected. The height grade of the mobile platform 200 can be detected,for example, in a manner shown and described above with reference toFIGS. 1, 5 and 6. One or more sensors 360 can be selected, at 330,according to the detected height grade, which sensors 360 can bepredetermined for the detected height grade. The selection of thesensors 360 is shown and described below in additional detail withreference to FIG. 14. At 340, certain information for operating themobile platform can be obtained. The information can include, forexample, a height of the mobile platform, a distance to an object 288(shown in FIG. 2), a displacement, a velocity and the like.

FIG. 14 shows another embodiment of the method 300 and illustrates thesensor selections for each of the four height modes of FIG. 4. In FIG.14, when a mobile platform 200 (shown in FIG. 15) detects a height to bewithin a first height grade, a first height mode 411 (shown in FIG. 4)can be selected, at 321. When the mobile platform 200 selects the firstheight mode 411, at 321, one image sensor 363 can be selected, at 322.In another embodiment, when the first height mode 411 is selected, at321, one image sensor 363 and a distance sensor 361 can be selected. Thedistance sensor 361 can be employed, for example, for determining adistance between the mobile platform 200 and an object 288 (shown inFIG. 2) of interest. Although shown and described as selecting onedistance sensor 361 and one image sensor 363 for purposes ofillustration only, other suitable types of sensors 360 can be selectedfor the first height mode 411.

The distance sensor 361 described herein can include, but is not limitedto, an ultrasonic detector and/or a laser detection device for detectinga distance.

In FIG. 14, the mobile platform 200 can detect an operating height of asecond height grade. Upon detecting the second height grade, the mobileplatform 200 can select a second height mode 412 (shown in FIG. 4), at323. When the mobile platform 200 selects the second height mode 412, at323, at least two image sensors 363 (shown in FIG. 15) can be selected,at 324. Each of the image sensors 363, selected for the second heightmode 412, can have a first resolution.

The mobile platform 200 can detect an operating height of a third heightgrade. Upon detecting the second height grade, the mobile platform 200can select a third height mode 413 (shown in FIG. 4), at 325. When themobile platform 200 selects the third height mode 413, at 325, at leasttwo image sensors 363 can be selected, at 326. Each of the image sensors363, selected for the third height mode 413, can have a secondresolution. The second resolution can be an enhanced resolution that canbe greater than the first resolution that is used under the secondheight mode 412.

The mobile platform 200 can detect an operating height of a fourthheight grade. Upon detecting the fourth height grade, the mobileplatform 200 can select a fourth height mode 414 (shown in FIG. 4), at327. When the mobile platform 200 selects the fourth height mode 414, at327, one image sensor 363 and one height sensor 362 can be selected, at328. The height sensor 362 can comprise, but is not limited to, abarometer 251 and/or a Global Positioning System (“GPS”) 253(collectively shown in FIG. 6).

FIG. 15 shows another alternative embodiment of a flying operationsystem 400 of the mobile platform of FIG. 2, wherein the processor 910(shown in FIG. 7) can be configured for selecting one or more sensors360 in accordance with the method 300 (shown in FIGS. 13 and 14).Turning to FIG. 15, a distance sensor 361, a height sensor 362 and oneor more image sensors 363 can be associated with, and communicate with,the processor 910. As described above with reference to FIG. 14, thedistance sensor 361 can include, but is not limited to an ultrasonicdetector 252 (shown in FIG. 7) and/or a laser detection device. Theheight sensor 362 can include, but is not limited to a barometer 251and/or a Global Positioning System (“GPS”) 253 (collectively shown inFIG. 7). The image sensors 363 can include, but are not limited to, abinocular imaging device 254 (shown in FIG. 2).

In some embodiments of the flying operation system 400, the processor910 can be provided for obtaining and processing the measurementsobtained from the sensors 360. Such measurements can include, but arenot limited to, a distance to an object 288 (shown in FIG. 2), theheight 121 and/or the disparity 122 (collectively shown in FIG. 1).Based on the measurements, the processor 910 can determine whichoperation mode can be selected and which one or more predeterminedsensors 360 can be included for the selected operation mode.

The described embodiments are susceptible to various modifications andalternative forms, and specific examples thereof have been shown by wayof example in the drawings and are herein described in detail. It shouldbe understood, however, that the described embodiments are not to belimited to the particular forms or methods disclosed, but to thecontrary, the present disclosure is to cover all modifications,equivalents, and alternatives.

What is claimed is:
 1. A method for selecting an operation mode of anunmanned aerial vehicle (UAV), comprising: detecting a height grade ofthe UAV, wherein detecting the height grade comprises determining aheight of the UAV and/or a disparity between first and second images ofa remote object from a perspective of the UAV; and selecting anoperation mode of the UAV from a plurality of height modes according tothe determined height grade, wherein the plurality of height modescomprises a first height mode and a second height mode, the first heightmode being a monocular mode and the second height mode being a stereovision mode.
 2. The method of claim 1, wherein the method furthercomprises categorizing the operation modes based on values of the heightand/or the disparity.
 3. The method of claim 1, wherein selecting theoperation mode of the UAV comprises: switching the operation mode of theUAV from the first height mode to the second height mode when the heightis greater than a first height threshold and the disparity is less thana first disparity threshold.
 4. The method of claim 1, wherein selectingthe operation mode of the UAV comprises: switching the operation mode ofthe UAV from the second height mode to the first height mode when theheight is less than a second height threshold and the disparity isgreater than a second disparity threshold.
 5. The method of claim 1,wherein selecting the operation mode of the UAV comprises: switching theoperation mode of the UAV from the first height mode to the secondheight mode when the height is greater than a first height threshold. 6.The method of claim 1, wherein selecting the operation mode of the UAVcomprises: switching the operation mode of the UAV from the secondheight mode to the first height mode when the disparity is greater thana second disparity threshold.
 7. The method of claim 1, wherein theplurality of height modes further comprises a third height mode and afourth height mode.
 8. The method of claim 1, wherein the second heightmode is a stereo vision mode with a first resolution, the plurality ofheight modes further comprises a third height mode, and the third heightmode is a stereo vision mode with an enhanced resolution.
 9. The methodof claim 8, wherein selecting the operation mode of the UAV comprises:switching the operation mode of the UAV from the second height mode tothe third height mode when the disparity is less than or equal to athird disparity threshold.
 10. The method of claim 8, wherein selectingthe operation mode of the UAV comprises: switching the operation mode ofthe UAV from the third height mode to the second height mode when thedisparity is greater than a fourth disparity threshold.
 11. The methodof claim 1, wherein the first height mode is a very low altitudemonocular mode, the plurality of height modes further comprises a fourthheight mode, the fourth height mode being a high altitude monocularmode.
 12. The method of claim 11, wherein selecting the operation modeof the UAV comprises: switching the operation mode of the UAV from thethird height mode to the fourth height mode when the height is greaterthan a third height threshold and the disparity is less than a fifthdisparity threshold.
 13. The method of claim 11, wherein selecting theoperation mode of the UAV comprises: switching the operation mode of theUAV from the fourth height mode to the third height mode when the heightis less than a fourth height threshold and the disparity is greater thana sixth disparity threshold.
 14. The method of claim 1, wherein themethod further comprises: assigning an initial mode to the operationmode of the UAV, the initial mode being selected from the plurality ofheight modes.
 15. The method of claim 14, wherein the initial mode is avery low altitude monocular mode.
 16. An apparatus for selecting anoperation mode of an unmanned aerial vehicle (UAV), comprising: abinocular imaging device associated with the UAV; and a processorconfigured to: detect a height grade of the UAV, comprising: determine aheight of the UAV and/or a disparity between first and second images ofa remote object from the perspective of the UAV; and select an operationmode of the UAV from a plurality of height modes according to thedetermined height grade, wherein the plurality of height modes comprisesa first height mode and a second height mode, the first height mode is amonocular mode and the second height mode is a stereo vision mode. 17.The apparatus of claim 16, wherein the processor is configured to:switch the operation mode of the UAV from the first height mode to thesecond height mode when the height is greater than a first heightthreshold and the disparity is less than a first disparity threshold.18. The apparatus of claim 16, wherein the processor is configured to:switch the operation mode of the UAV from the second height mode to thefirst height mode when the height is less than a second height thresholdand the disparity is greater than a second disparity threshold.
 19. Theapparatus of claim 16, wherein the processor is configured to: switchthe operation mode of the UAV from the first height mode to the secondheight mode when the height is greater than a first height threshold.20. The apparatus of claim 16, wherein the processor is configured to:switch the operation mode of the UAV from the second height mode to thefirst height mode when the disparity is greater than a second disparitythreshold.